OBJECTIVES: An increase in opioid utilization during pregnancy in recent years has contributed to a surge in the incidence of Neonatal Abstinence Syndrome (NAS). The objective of the study was to compare the pattern and intensity of opioid utilization during pregnancy in deliveries with and without NAS. METHODS: : We examined women in a commercial claims database for years 2011-14 who filled an opioid prescription during pregnancy for a non-cancer indication. Pregnancies were stratified into pre-term and full-term. NAS was identified using ICD-9 code 779.5. For each prescription, the morphine equivalent dose (MED) was calculated, and the average daily MED was estimated on a bi-weekly basis for each patient during the gestation period. We matched one NAS delivery to one non-NAS delivery on eight risk factors—including cumulative opioid use in the first two trimesters—to create a matched set that theoretically differed in its risk for NAS through a difference in opioid utilization in the last trimester. RESULTS: : We found 314 cases of NAS in 61,568 pregnancies (5.10 cases per 1,000 deliveries). In the unmatched analysis, we found that compared to non-NAS pregnancies, NAS pregnancies had a significantly higher average daily MED during the gestation period (+36 mg MED, p<0.01). In NAS pregnancies, we noted a decrease in the average daily MED following the onset of pregnancy, which remained stable up until the third trimester where it subsequently increased. In the matched analysis, the mean MED in the third trimester was higher in the NAS group compared to the non-NAS group (+2.41 mg MED). Our findings in the pre-term pregnancy group were similar. CONCLUSIONS: : While opioid exposed patients who developed NAS made a concerted effort to decrease their opioid utilization following the onset of pregnancy, opioid utilization remained high throughout the gestation period. Near-term opioid use was associated with NAS.